The present invention relates to a process for converting solar energy into useful heat which may serve, e.g., for heating air or water; further, the invention relates to an apparatus for performing this process.
Apparatuses, i.e., the so-called solar collectors, have already been proposed which substantially consist of a heat-conductive and radiation-absorbing flat-shaped body (absorber) comprising a surface which faces the source of radiation (absorption surface) and which is blackened in order to achieve maximum absorption of the incident radiation energy. On the other hand, the absorption surface is covered with glass plates in order to reduce heat losses caused by reflection of thermal energy from the absorption surface.
At the back of the absorber, the energy absorbed by the absorber normally is transferred to a suitable medium (heat carrier) and conducted away. The heat carrier is conveyed to the back of the absorber and drawn off from it in a cycle. Circulation of the heat carrier usually is effected by means of a system of tubes and appropriate pumps. These devices involve the risk that in the event of a fault in the circulating system, for example in the case of a pump breakdown or loss of heat carrier by leakage or pipe burst, the absorber may be overheated and completely destroyed. In principle, it is possible to take the necessary precautionary measures, but such measures require expensive technical equipment and are very costly.
The transfer of heat from the absorber to the heat carrier poses a further problem in known solar collectors. Since the contacting surface between these two components must be as large as possible, a technically expensive system is required. Further, in the case of a heat carrier extending over a large area, the question of good thermal insulation presents difficulties.